Polymerizing lactam to polylactam with a substituted phosphorane cocatalyst



United States Patent 3,345,340 POLYMERIZING LACTAM T0 POLYLACTAM WITH A SUBSTITUTED PHOSPHORANE COCATALYST Harold G. Brouns, Woodbury, N.J., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Oct. 1, 1964, Ser. No. 400,881

20 Claims. (Cl. 260-78) ABSTRACT OF THE DISCLOSURE Polymerizing lactams, preferably having 3 to 12 carbon atoms in the lactam ring, to polylactams at a temperature below the melting point of the resulting polylactam employing as cocatalyst substituted phosphoranes represented by the structures R PF NR (R N) PF (R PF )-(R NH R PF and V wherein R represents methyl or ethyl, R represents a monovalent organic radical of up to 20 carbon atoms and fluorine, R represents a monovalent aliphatic or alicyclic radical of up to 20 carbon atoms or a divalent aliphatic radical of up to 20 carbon atoms in which both valence bonds are joined to an adjacent nitrogen atom to form a cyclic structure, R is a monovalent organic radical of up to 20 carbon atoms, a is an integer from 1 through 3 and the sum of a and b is 5.

This invention relates to an improved process for the anionic polymerization of lactams. More particularly,

this invention relates to an improved process for the rapid anionic polymerization of lactams at temperatures below the melting point of the resulting polyamide wherein substituted phosphoranes catalysts.

The polymerization of caprolactam to give a polyamide, 6 nylon, has been known for many years. The earliest processes described for this polymerization were quite slow, requiring several hours. More recently, it has been disclosed that the base-catalyzed polymerization of lactams for example, caprolactam, can be made especially fast by the addition of certain cocatalysts derived from organic and inorganic acids ofvparticular typesQ'Particularly efiective cocatalystsfor the anionic polymerization are employed as novel coof lactams known to the art include acylating agents and acyl compounds, for example, acyl halides, anhydrides, imides, and the like. Other classes of cocatalysts which have been disclosed includevorganic'isocyanates and substituted ure as.

The present invention provides a process for the poorganic radical of up to 20 carbon atoms or fluorine, R is a monovalent aliphatic or alicyclic radical of up to 20 carbon atoms, or a divalent aliphatic radical of up to 20 carbon atoms in which both valence bonds are joined to an adjacent nitrogen atom to form a cyclic structure, R is a monovalent organic radical of up to 20 carbon atoms, a is an integer from 1 through 3, and the sum of a and b is 5.

A representative list of compounds coming within the scope of the present invention that are useful as cocatalysts in the anionic polymerization process include, among others, the following:

(piperidyl) PF (n-dodecylphenyl NPF (l-azacyclododecyl)PF oanarrm: s

' l,3-dimethyl-2,4-dibenzyl-2,2,4,4-tetrafiuoro-1,3,2,4-

diazadiphosphetidine I,3-dimethyl-2,4-dicyclohexyl-2,2,4,4-tetrafluoro1,3,2,4-

diazadiphosphetidine 1:methyl-3-ethyl-2-phenyl-4-ethyl-2,2,4,4-tetrafluoro 1,3 ,2,4-diazadiphosphetidine 1-ethyl-3-methyl-Z-propyl-4-isoamyl-2,2,4,4-tetrafluoro- 1,3 ,2,4-diazadiphosphetidine 1-ethyl-3-methyl-2,4-diphenyl-2,2,4,4-tetrafluoro- 1,3,2,4-diazadiphosphetidine 3 with an R SiN(R)Si(R component wherein R and R are defined above and c is an integer of 4 or 5 and the sum of c and d is 5. The reaction temperature is maintained between about and about 150 C., with the pre- 'ferred range being from about 20 to about 50 C. If the reaction temperature is higher than the boiling point of any reactant the reaction is then conducted in a sealed vessel of such construction as to withstand the pressure generated. Preferably, the ratio of the two components is stoichiometric; however, any ratio can be used. The

yield is determined by the quantity of the reactant present in the lesser quantity.

If the diazadiphosphetidine cocatalyst has different substituents on the two nitrogen atoms or on the two phosphorus atoms it can be prepared by reacting a mixture of components. For example, if 1-methyl-3-ethyl-2- phenyl-4-ethyl-2,2,4,4-tetrafluoro 1,3,2,4 diazadiphosphetidine is desired a mixture of 3 s z s a a s 4 and C H PF is heated and reacted. The components of the resulting reaction products are then separated by distillation.

Heptamethylsilazane (CH SiN(CH )Si(CH is pre pared from (CH SiCl and CH NH by a method given in Inorganic Syntheses, vol. V, p. 58, McGraw-Hill, 1957. For the preparation of other disilazanes, a similar procedure is used with the substitution of the appropriate chlorosilane for trimethylchlorosilane and the appropriate amine for methyl amine. For example,

resists hydrolysis in boiling water for several hours. On the other hand, the corresponding chloro compounds are hydrolyzed almost immediately by water at room temperature.

The preparation of diazadiphosphetidines is more completely described in coassigned, copending application Ser. No. 301,985, filed Aug. 14, 1963.

The compounds of the types R PF NR (R N) PF (R PF )*(R NH are prepared by reacting a component having the general formula R PF with a compound having the formula (R N) R at a temperature between 0 and 150 C. in a stoichiometric ratio and wherein R, R and R have the meanings given hereinbefo'r'e, R is R or R N, R is hydrogen or SiR and n is the integer 2 or 3.

For example, R PF NR can be made in two ways. 'WhereR is fluorine:

(1) 2PF +2R NH (R N)PF (R NH (PR PF +R NSiR R NPF+R SiF Where R is an organic radical:

Likewise (R N) PF can be made by the following reaction:

Preparation of the (R PF anion'salts is accomplished as described above.

Preparation of 'these compounds is more fully described in coassigned copending application Ser. No. 310, 128, fil ed Sept. 19, 1963, now U.S. Patent 3,300,503.

The RQPF compounds are well known and are prepared as described in Chemistry and Industry (London) 1962, 1868.

When R R R and R are hydrocarbon radicals their nature is not critical. However, they should not contain substituents which are reactive with the lactam polymerization system.

The following specific examples are given hereinbelow that describe in detail methods generally applicable for making cocatalyst compounds of the type described and used in the anionic polymerization of lactams in the present invention. I

EXAMPLE 1 Preparation of a diazadiphosphetidine 18.4 parts of phenyltetrafluorophosphorane is added slowly, with stirring, to 13.15 parts of heptamethyldisilazane in a reaction vessel maintained at 50 C. and protected against atmospheric moisture. After about half of the fluorophosphorane is added a gas is evolved which is identified as trimethylfluorosilane by infrared absorption. The quantity of this gas amounts to of theoretical yield. After all of the fluorophosphorane is added volatile material is removed at 0.1 mm. pressure and 30 C. 3.5 parts of unreacted phenyltetrafluorophosphorane is recovered. The remaining solid melts at 161 C. After two recrystallizations from benzene the melting point is raised to 162 C. indicating a high degree of purity in the crude product. The compound is identias compared to 350.2 theory.

The infrared'spectrum as a solid in a KBr pellet is as follows: 3060-(w), 2940 (m), 2890 (vw), 2816 (w), 1820 (w), 1593 (w), 1486 (m), 1440 (s), 1420 (vw), 1383 (W), 1314(m), 1230, 1172, 1123 (vs), 975 (m), 928 (w), 879, 849 (vw), 835, 829 (vs), 768, 760(vs), 744, 735 (vs) 691 (vs),'605(vs), 539*(vs), 503, 484 (s).

The ultraviolet spectrum (0.516 mg./rnl. in cyclohexane) maxima at 257, 264 and 271 m extinction coeflicient' 13 .060.

Attempted hydrolysis by heating in water at C.

'for 3 hours fails. The product still has a melting point of 162C. and the'infrared spectrum is the same.

EXAMPLE '2 Preparation of a R PF NR compound Phenyltetrafiuorophosphorane (40.5 parts) is added dropwise with stirring to 20.2 parts of dimethyl-bis(N,N- diethylamino)silazane. An exothermic reaction is observed but the temperature is'held below 40 C. by cooling.

After the addition the mixture is stirred for 40 minutes at 90 C. Vigorous evolution of gas (dimethyldifluorosilaneidentified by infrared) occurs above 50 C. and an 84% yield of this gas is collected in a Dry Ice trap. The residue is distilled to give an 89% yield of C H PF N(C H boiling at 50/0.08 mm.; n 1.4695.

v 7 EXAMPLE 3 Preparation of a (R PF salt A three-necked flask is equipped with a gas inlet tube, a thermometer, and a reflux condenser with a drying tube. The system is flushed with dry nitrogen and charged with a solution of 44 parts of phenyltetrafluorophosphorane in 105 parts ether. Dimethylamine (11.0 parts), dried by passing it through a tube filled with sodium hydroxide pellets, is bubbled through the solution at C. (2 hr.) A precipitate is formed temporarily but disappears upon removal of the ether solvent by distillation at atmospheric pressure. The remaining two-phase liquid mixture is distilled in vacuo through an 8-in. helix-packed column. Material boiling at 4849 C./0.4 mm.; n =1.4796 is collected first. Yield of 'C H PF N(CH is 19.6 parts (79% The higher boiling residue solidifies on standing. It is distilledat higher temperature, again solidifying readily after the distillation. B.P. 128-129 C./0.15 mm. Colorless solid, M.P. 0a., 50 C.; yield of Analytical data.1. C H PF N(CH Calcd.: C, 45.9; H, 5.3; F, 27.2; N, 6.7; P, 14.8. Found: C, 45.8; H, 5.5; F, 27.8; N, 7.0; P, 14.7.

EXAMPLE 4 Preparation of a (R N) PF compound A 3-necked flask is equipped with a gas inlet tube, a reflux condenser with a drying tube, and a thermometer. Under a countercurrent of nitrogen, a solution of 8.25 parts of diethylamine in 75 parts pentane is then placed into the flask. After cooling to ca. 50 C., a total of 8 g. (0.063 mole) of phosphorus pentafiuoride is passed through the solution. No noticeable reaction takes place, but unreacted PF is not observed. A viscous oil separates as the temperature is gradually allowed to rise to room temperature. The separated liquid is decanted and distilled to'remove pentane. The higher boiling product comes over between 64-86 C./ 18 mm., mainly atthe latter temperature'. Purity by VPC was 95-97%, n =1.4046.

Analysis.'Calcd. for [(C H N] PF C, 41.3; H, 8.7; N, 12.1. Found: C, 41.3; H, 8.9; N, 11.4.

Molecular weight (mass spectroscopy).--Significant' peaks at 233 (parent), 161 (parent less N(C H etc.

IR Spectrum (liquid).2980 (s); 1486, 1470, 1450 (m); 1379, 1349 (s); 1297 (m); 1207, 1184 (vs); 1090, 1072 (s); 1041 (vs); 961, 942 (s); 839, 807 (vs); 736 (vs); 683 (w).

F NMR Spectnum (liquid).Doublet of doublets, J =751 cps., I =46 p.p.m., 6 (CFCl int.)=+59.5 p.p.m.; doublet of triplets, J =875 cps.; 6 (CFCl +73.-9 p.p.m. This pattern is typical of RPF NF structures. J a 7 Accordingly, the above illustrates methods for preparing the compounds used as cocatalysts in the polymerization reaction of the present invention.

The polymerization process of this invention is pareral, this temperature range is from about 25 C. to about 200 C., depending on the particular lactam or lactams employed. The preferred polymerization temperature is below about 150 C. with lactams having less than 6 carbon atoms in the lactam ring. Caprolactam is readily polymerized by the process of this invention at temperatures between 100 and 200 C. with 150 C. being a convenient and preferred operating temperature. Lactams having more than five carbon atoms are preferred for the practice of this invention and e-caprolacta-m is especially preferred.

The lactam-base salts, i.e., anioniccatalysts, used in the process of this invention are the reaction product of a strong base and a lactam. Generally, the lactam to be polymerized is used for the preparation of the lactam-base salt but if desired, the lactam-base salt can be prepared from one lactam and used in the polymerization of still another lactam.

The strong base employed to form the lactam-basesalt,

i.e., anionic catalyst, may be an alkali metal, an alkaline earth metal, or a strongly basic derivative of one of these metals such as hydroxide, alkoxide, hydride, alkyl, aryl, or amide. All of these bases are strong enough to convert the lactam to its iminium salt. Thus, sodium hydroxide,

potassium hydroxide, lithium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, sodium methoxide, lithium hydride, sodium hydride, sodium methyl, sodium ethyl, sodium phenyl, sodium naphthyl, sodamide, and the like are suitable strong bases for the preparation of the anionic catalyst. Accordingly, the anionic catalyst is prepared by heating the lactam with a strong base at a temperature between about 25 and 225 C.

The strong base used to form the catalyst can be, if desired, diluted with inert materials such as mineral oil or other hydrocarbon materials for ease of handling. Sodium hydride is particularly susceptible to attack by moisture and the use of a mixture of NaH and an inert diluent, instead of pure NaH, is effective in making t-the addition of catalyst both safer and easier. HB40, a partially hydrogenated terephenyl, is a particularlyv suitable diluent. The base may be added to the total lactam which is to be polymerized, or, to a portion of the lactam which is to be polymerized and this portion of the lactam containing the lactam-base-salt, i.e., anionic catalyst, is added to more of the lactam later. Little or no polymerization occurs during the preparation of the anionic catalyst, which is carried out at a temperature between the melting point of the lactam and about 225 C. The time required for this step in the process varies and depends upon the strength of the base employed, the proportion added, and the temperature chosen and may take from a few seconds to several hours. Preferably, the lactam, and likewise the base with which the lactam is reacted, should be substantially anhydrous. The concentration of the baseis betweeL about 0.1 to about 10 mole percent based on the lactam polymerized. Proportions in the higher end of this range produce lower molecular weight polyamides, so optimum proportions for most purposes are from about 0.1 to 5 mole percent of the strong base.

It might be mentioned that for the optimum operation of the'process-of this invention, an inert gas such as nitrogenis bubbled through the molten lactam during the initial reaction of the base with the lactam to form the ticularly effective for rapidly producing high molecular anionic catalyst, in order to remove any low molecular Weight compound formed such as water and in order to prevent oxidation. Alternatively, the reaction of the lactam with the strong base may be carried out under reduced pressure in which case the low molecular weight compound is distilled from the lactam. Procedurally the cocatalyst used in the process can be added to the lactam containing the anionic catalyst, or equally well, the cocatalyst can be dissolved in a separate portion of the lactam and the two portions of lactam mixed at the time the polymerization is desired.

The process of this invention is useful in rapidly preparing cast articles of any size and shape from lactams and may be employed to obtain unusual shapes which would be diflicult, if not impossible, to obtain by conven- The process of this invention likewise can be carried out as a coating process, in which the lactam solution containing an anionic catalyst and a substituted phosphorane derivative cocatalyst is applied as a liquid to tional molding of prepolymerized polyamides. The procmetal, plastic, wood or the surface of a web, such as paper ess has the additional advantage of not requiring high or a textile and then permitted to polymerize to the polytemperatures and high pressures normally required in amides and thus form a coating of polyamide film on 2. injection molding techniques and similar processes to prosubstrate. 'duce cast articles. Therefore, simpler lighter weight molds The following examples more thoroughly illustrate the may be employed and faster cycles can often be obtained anionic polymerization reaction of lactams in the presence in the preparation of large shaped articles. The entire of cocatalyst wherein parts given are by weight. process can be carried out in a mold. Alternatively, the EXAMPLES 5 THROUGH 25 lactam solution containing the anionic catalyst and a second portion of the lactam solution containing the co- Pr ced r A i i can be than g i g Into eCaprolactam (22.6 parts) is melted, heated to 150 m9 l g fi 3 i trans m0 P C., and sparged 1015 minutes with nitrogen. The base tam t .eslre .artlc e m any $126 at a Very (for example, sodium hydride, 3 mole percent based on f i It IS posslple to employ t prpcess thls lactam) is added and the mix sparged an additional 5 inventlon m {mfny fi 9 'i s m Winch the minutes and the anionic catalyst, i.e., lactam-base salt is i i i z t e i i q formed. The cocatalyst (for example, (C H NPF 0.6 9 3 t 3 i am e ys i mole percent), is added, the mix sparged for 30 seconds g en extrtu f 3? 1101115 with nitrogen and allowed to stand under a nitrogen o dammg an ex m a e W 10 15 PO ymenze as 18 blanket at 150 C. until polymerization occurs. The no f??? f b1 th flow time is the time within which the mix becomes so of gi i g gg gi g j j Fi g i viscous that no p rceptible flow occurs when the Polymample, if desired, glass mats or mats of synthetic fibers i ii g i i at an angle of 45 and 1S 2 can be impregnated with the solution and rapidly cured. m n s m 18 6 amp Similarly, finely-divided fillers can be suspended in the Procedure B fiiiiiffii tiisffiiiii riii ii itiil 1003320355232 e-Caprolactam (11-3 Parts) is melted, heated w a a 7 and the like may also be employed. The process of this g; jpafrglsdgvlth i 35? f: gg gz i g zfi g i g invention contemplates the use of the process under all 6 amp e 1 i 1 Spar; of the above Conditiom with nitrogen for minutes and the amonic catalyst, 1.e., The process of this invention can be conducted in the lactam'b'ase salt is formed Anotoher Porno of .presence of a gas-generating material to give foamed lifctam 1S meltei heated to 150 and sP Wlth plastic articles. The gas-generating material can be a 10W nltrogen for 10*15 The cocatalyst for mpl boiling liquid or an unstable compound which releases e 5 3 2 s)2 15 added and the mlX aged 30 vgas when heated. Representative gas-generating materials tes at 150 C. The two portions are then mixed and the are, for example, allylic azides such as dodecenyl azide, polymerization occurs. bis(azidomethyl)durene, benzyl azide, p-methylbenzyl Procedure C azide; azo compounds such as azobis(isobutyronitrile); low boiling hydrocarbons such as ethane, propane, bu- The same as procedure B, except that the two portions tane,-pentane and hexane and the like. of lactam are aged only 5 minutes before mixing.

Mol., Mol., i No Flow Example No. Cocatalyst percent Base percent Time Procedure (min) 0flH5PFi 0.6 NaH 2.7 10 A CGH5PF4 0.6 NaH 3.0 5 A. iso-C5H17PF4 0.6 NaH 3.8 1 A (CaHshPFa 0.6 NaH 3.3 5 A (CaH5)(I1-C4H9):PF2 0.4 NaH 1.5 11 A. (1l-C4H9)3PF2 0.6 NaH 2.7 5 A FflIf-N-CHS 0.4 NaH 3.0 4 A H3ON-PF3 12 F, 0.4 NaH 3.0 2.5 A

02115 NOH HsCN-?C2Ha 13 1;; 0.4 NaH 3.0 2.7 A

C H P-NCHs H3CN]|? C6H5 CzH5PF3N(CzH5)1 0.4 NEH 3.0 3 A CuH5PFzN(CH3)z 0.4 NaH 3.0 7 A CoH5PF N(C2H5)z 0.4 NaH 3.0 2.4 A ((CH;)zNH )+(C@HsPFs)- 0.4 NaH 3.0 8.7 A ((02H5)2NH)+(OuH5PF5)' 0.4 NaH 3.0 7 A (O2H5)2NPF4 0.6 NaH 3.0 2 A F|z 0.6 NaH 3.0 3.2 A p-FzC CaH4PNCHs H5ONPCOH4C F -p M01., M01., NoFlow Example No. Coeatalyst percent Base percent Procedure ((OzHmNhPFs 0. 6 NaH 3.0 4.1 A ((C2H5)2N)2PF3 0.5 NaH 3. 5 22 B CGHEPF3N(C2H5)I 0. 5 NaH 3. 5 5. 9 B ((CzHs)2N)2PFa 0. 5 NaH 3. 5 44. 7 O C smrramomm 0.5 NaH 3. 5 2. 7 C

EXAMPLES 26-28 The procedure for the following examples is the same as that given in procedure'A, except that other lactams and mixtures thereof are substituted for e-caprolactam on an equimolar basis.

In Example 28 sodium methoxide was substituted for sodium hydride on an equimolar basis with equivalent 2 results, wherein R is selected from the group consisting of .methyl Example Mol., Mo1., No Flow No. Lactam Cocatalyst percent Base percent Procedure Time (min) 26 Laurnhntam (C2H5)2NPF4 0.4 NEH/Qua". 1.2 A 4.2

27 do F, v 0.4 NaH/oi1 2.0 A 19 oimi-N-crn NaCN- -C2H5 t.

28 {g, %g% gg; }(C2H6)2NPF4, 0.2 NaH/oil 0.6 A

What is claimed is: and ethyl, R is selected from the group consisting of a 1. In a process for the polymerization of anhydrous 35 monovalent organic radical of up to 20 carbon atoms and lactams to polyamides which comprises heating said fluorine, R is selected from the group consisting of a lactam to a temperature below the melting point of the monovalent aliphatic and alicyclic radical of up to 20 carresulting polyamide in the presence of a lactam-base salt bon atoms and a divalent aliphatic radical of up to 20 and a cocatalyst, the improvement which comprises using carbon atoms in which both valence bonds are joined to as a cocatalyst a substituted phosphorane selected from 4 an adjacent nitrogen atom to form a cyclic structure, R the group consisting of compounds define-d by the strucis a monovalent organic radical of up to 20 carbon atoms, tures R PF NR (R NMPF (R BF )"(R NH a is an integer from 1 through 3 and the sum of a and b R -PF and is 5.

R '5. The process of claim 4 wherein the lactam is caprolactam. F2PN R 6. The process of claim 4 wherein the lactam is laurop R1 lactam.

7. The process of claim 4 wherein the lactam is a mixture of at least two lactams. wherein R is selected from the group consisting of methyl 8. The process of claim 4 wherein the lactam-base salt and ethyl, R is selected from the group consisting of a is the reaction product of caprolactam and sodium hymonovalent organic radical of up to 20 carbon atoms and dride. 1 fluorine, R is selected from the group consisting of a 9. The process of claim-4 wherein the lactam-base salt monovalent aliphatic and alicyclic radical of up to 20 is the reaction product of caprolactam and sodium methcarbon atoms and a divalent aliphatic radical of up to 20 oxide. carbon atoms in which both valence bonds are joined to 10. The process of claim 4 wherein the amount of coan adjacent nitrogen atom to form a cyclic structure, R catalyst is from about 0.2 to 1 mole percent. is a monovalent organic radical of up to 20 carbon atoms, 11. In a process for the polymerization of anhydrous a is an integer from 1 through 3 and the sum of a and b lactams having from 3 to 12 carbon atoms in the ring is 5. which comprises heating said lactam to a temperature 2. The process of claim 1 wherein the lactam is caprobelow the melting point of the resulting polyamide in lactam. the presence of a lactam-base salt made from about 0.1 3. The process of claim 1 wherein the amount of coto about 10 mole percent base, based on the lactam, and catalyst is from about 0.05 to 5 mole percent, based on a cocatalyst, the improvement which comprises using as the lactam being polymerized. a cocatalyst from about 0.05 to 5 mole percent, based on 4. In a process for the polymerization of anhydrous the lactam being polymerized, of a substituted phosphorlactams having from 3 to 12 carbon atoms in the ring ane having the structure R1PF3NR22 wherein R is selected which comprises heating said lactam to a temperature from the group consisting of a monovalent organic radical below the melting point of the resulting polyamide in the of up to 20 carbon atoms and fluorine and R is selected presence of a lactam-base salt made from about 0.1 to from the group consisting of a monovalent aliphatic and about 10 mole percent base based on the lactam, and a alicyclic radical of up to 20 carbon atoms in which both cocatalyst, the improvement which comprises using as a valence bonds are joined to an adjacent nitrogen atom cocatalyst from about 0.05 to 5 mole percent, based on to form a cyclic structure. the lactam being polymerized, of a substituted phosphor- 12. The process of claim 11 wherein the lactam is ane selected from the group consisting of compounds caprolactam.

16. In a process for the polymerization of anhydrous lactams having from 3 to 12 carbon atoms in the ring which comprises heating said lactam to a temperature below the melting point of the resulting polyamide in the presence of a lactam-base salt made from about 0.1 to 10 mole percent base, based on the lactam, and -a cocatalyst, the improvement which comprises using as .a cocatalyst from about 0.05 to 5 mole percent, based on the lactam being polymerized, of a substituted phosphorane having the structure (R N)PF wherein R is selected from the group consisting of a .monovalent aliphatic and alicyclic radical of up to 20 carbon atoms and a divalent aliphatic radical of up to 20 carbon atoms in which both valence bonds are joined to an adjacent nitrogen atom to form a cyclic structure.

14. The process of claim '13 wherein the lactam is caprolactam.

'15. -In a process for the polymerization of anydrous lactams having from 3 to 12 carbon atoms in the ring which comprises heating said lactam to a temperature below the melting point of the resulting polyamide in the presence of a lactam-base salt made from about 0.1 to about 1-0 mole percent base, based on the lactam, anda cocatalyst, the improvement which comprises using as a cocatalyst from about 0.05 to 5 mole percent, based on the lactam being polymerized, of a substituted phosphorane having the structure (R 'PF )(R N I-I wherein R is selected from the group consisting of a monovalent organic radical of up to 20 carbon atoms and fluorine and R is selected from the group consisting of a monovalent aliphatic and alicyclic radical of up to 20 carbon atoms and a divalent aliphatic radical of up to 20 carbon atoms in which both valence bonds are joined to an adjacent nitrogen atom to-form'a cyclic structure.

16. The "process of claim 15 wherein the lactam is caprolactam.

17. In a process for'the polymerization 'ofanhydrous lactams having from 3 'to '12 carbon atoms in the ring which comprises heating said lactam to a temperature below the melting point of the resulting polyamidein the presence of a lactamabase salt made from about 0.1 to about 10 mole percent base, based on the lactam, and a cocatalyst, the improvement which comprises using as a cocatalyst from about 0.05 to 5 mole percent, based on the lactam being polymerized, of a substituted phosphorane having the structure RQP-F wherein R is a monovalent organic radical of up to 20carbon atoms, a is an ,Linteger-from 1 through 3 and the sum of a and b is 5.

v .18. The process of claim 17 wherein the lactam is caprolactam.

19. In a process for the polymerization of anhydrous lactams having from 3 .to 12 carbon atoms in the ring which comprises heating said lactam to a temperature below the melting point of the resulting polyamide in the presence of a lactam-base salt made from about 0.1 to 10 mole percent base, based on the lactam, and a cocatalyst, the improvement which comprises using as a cocatalyst from about 0.05 to 5 mole percent based on the lactam being polymerized of a substituted phosphorane having the structure R1 F21|)N--R R-ILl-PR F wherein R is selected from the group consisting of methyl and ethyl and R is selected from the group consisting of a monovalent organic radical of up to 20 carbon atoms and fluorine.

20'. The process of claim 19 wherein the lactam is caprolactam.

References Cited UNITED STATES PATENTS 3,028,369 4/1962 Butler et :al 26078 3,232,892 2/1966 Fisher 260---7-8 3,246,032 4/ 1966 'Schmutzler 260-48 WILLIA'M SHORT, Primary Examiner.

H. D. ANDERSON, Assistant Examiner. 

1. IN A PROCESS FOR THE POLYMERIZATION OF ANHYDROUS LACTAMS TO POLYAMIDES WHICH COMPRISES HEATING SAID LACTAM TO A TEMPERATURE BELOW THE MELTING POINT OF THE RESULTING POLYAMIDE IN THE PRESENCE OF A LACTAM-BASE SALT AND A COCATALYST, THE IMPROVEMENT WHICH COMPRISES USING AS A COCATALYST A SUBSTITUTED PHOSPHORANE SELECTED FROM THE GROUP CONSISTING OF COMPOUNDS DEFINED BY THE STRUCTURES R1PF3NR2**2, (R2**2N)2PF3, (R1PF5)-(R2**2NH2)+, RA3PFB AND 